The present invention relates generally to fuel feeders for stokers and more particularly to a new and improved multi-fuel feeder distributor that has the capability of feeding into a furnace and distributing over a grate coal and a second fuel, such as wood or a waste fuel, in combination or separately.
Prior art stokers which have the capability of feeding into the furnace and distributing over a grate coal and a second fuel in combination or separately have generally comprised two or more separate feeders at separate feed points. U.S. Pat. No. 2,228,751 (Bros), does disclose a fuel feeder which feeds a refuse fuel and coal at a single feed point, but the Bros device has several disadvantages. In the Bros device, the fuel is mixed prior to being thrown into the furnace chamber by the rotor. The size and weight of refuse fuel and coal are rarely the same. The rotor speed used in the Bros device would have to be an average speed and would not be correct for either fuel at the throw. Packing in the rotor housing will occur as the lighter refuse fuel, usually moist, is mixed at the rotor with the coal. Also, the mixing of the refuse and the coal prior to throw may cause an incorrect coal distribution on the grate due to the lighter fuel agglomerating on the pieces of coal or with other refuse fuel. Since an even coal bed is essential to efficient combustion in the stoker, such a problem is very significant in stoker fuel feeding applications. Other distinguishing features will be illustrated in the following specification and drawings.
One object of the present invention is to feed a second fuel, such as wood, bagasse, bark, municipal refuse, any other cellulose or waste fuel, or other fine, dry particulate fuels, in combination with coal into a furnace onto a grate, while at the same time not interfering with the coal feed providing a uniform coal bed for efficient combustion on the grate.
Another object is to provide separate control of the coal feed and the second fuel feed to permit optimum usage efficiency and flexibility of the stoker.
Combining the feeders into one opening not only requires fewer feeder openings into the furnace, but also provides the advantage of lower furnace air leakage. Additionally, the capital cost of converting a stoker having the capability of feeding only one fuel into a multi-fuel stoker is significantly less with the present invention, since both fuels are fed through the same opening into the furnace, this opening being approximately at the same location and of the same size as that required for a standard coal feeder when coal is the only fuel.
A further object is to provide a multi-fuel feeder having minimum furnace air leakage and a potential for lower positioning of the feeder relative to conventional feeders. A lower position would provide better fuel distribution over the grate surface of a stoker and better potential use of furnace volume.
The waste fuel feeding portion of the feeder consists of a chute for conveying the fuel by gravity to an air swept distributor spout and has several advantages independent of the multi-fuel combination. The waste fuel chute includes a counterbalanced damper which has the object of aiding in the distribution of the waste fuel, no matter how fine, across the width of the chute, which damper also serves as a back draft damper to prevent blow back from the furnace to the fuel storage system. Also, the damper may be positioned to completely close the waste feed chute if only coal is fed to the multi-fuel feeder distributor.
The damper plate is adjustable and can be locked in a fixed position to result in a narrow venturi throat. A further advantage of the present invention occurs when the feeder is used in this capacity to feed fine, dry fuels. Auxiliary steam jets are included to increase the velocity of the fine, dry fuel through the venturi throat to prevent blow back and assure injection of the fuel into the furnace faster than flame can propagate up the chute.
The air swept spout also supplies energy to feed the fuel over the entire grate from front to rear and side to side and has the further object of preventing sticking and plugging of the fuel in the chute.
The refuse chute spout includes a distribution air discharge slot at the discharge point where the fuel leaves the spout to enter the furnace. This air stream provides the advantage of accelerating the fuel entering the furnace to improve distribution of the fuel over the grate and advance the fuel to the opposite portion of the furnace.
A further object of the invention resides in the use of water cooling at the hopper feed throat to reduce the reflected heat from the furnace to protect the feeder parts from damage and reduce the potential of heat blow back into the chute.
Additional advantages of the present invention include a multi-air distribution system with deflector dampers to allow adjustment of distribution of the fuel and a continual variable air flow by means of a rotating damper, having a minimal air flow adjustment capability, to give variable distribution of waste fuel into the furnace onto an even bed of coal.
Other objects and advantages of the instant invention will be apparent in the following specification, claims and drawings.